Population pharmacokinetic and pharmacodynamic (PK-PD) parameters of Erwinia Chrysanthemi (ERW) asparaginase (ASNase) using the fused first-order elimination and Michaelis-Menten (MM) limited physiological model

Abstract

13010 Background: Using the linear PK first order (FO) compartmental approach, the methodical and computational uniformity in modeling various linear systems (ERW) is the dominant characteristic of the population PK analyses. However, saturation of the enzymatic reaction results in nonlinear kinetics based on the MM equation, i.e., the deamination of ASN by ERW, which complicates the PK-PD model. The PK with FO & the MM PK-PD model is theoretically better when single dose of ERW is given. To simulate the PK-PD data and to project patient (pt) data using this model, we used simultaneous integration of the FO+MM equations. Methods: In the 1990’s, ERW was used in pediatric ALL pt (n=23, 1st cohort evaluated for PK-PD). The current study was started to assess if the parallel MM+FO (MM+FO) PK-PD model fit the limited ERW (25K) data better than the MM model, and to validate the MM+FO model and its population parameter estimates. Results: The population PK-PD model best-fitted serum ERW & ASN-time pairs obtained in 23 and from 5 pediatric pt with ALL, using nonlinear mixed-effects modeling (NONMEM). The validity of the MM+FO population PK-PD model and the estimated parameters were tested using the naive prediction method. Patients were administered ERW 6K or 25 K IU/m2 when allergy to E. coli formulations appeared. High correlation between ERW peak serum levels calculated from limited individual pt’ KM (900 μM) & Vmax values in 5 pediatric pt (2nd cohort) and the observed ERW trough levels & its substrate (ASN) were found. The T1/2 averaged 16 hr (25K ERW), and the trough level of 0.1–0.2 IU/ml was correlated with ASN <3 μM. These PK-PD parameters validated those obtained from the 1st cohort. When simulations on population parameters were conducted, the MM+FO predicted the multiple dose steady-state serum ERW & ASN levels nicely. Therefore, the MM+FO model was clearly superior to either the FO or the MM PD models. Moreover, simulations compared favorably ERW 25K Q2 days x3 doses & x2 weeks vs. Pegaspargase 2,5K Q2 weeks. Conclusions: The NONMEM PK-PD model for ERW fitted the simultaneous analyses of data from different doses and regimens better than either standard Two-stage or MM could. No significant financial relationships to disclose.